Extending the optical spectrum of an optical network

ABSTRACT

Systems and methods include, for operation on an optical fiber in an optical network with the optical fiber having extended optical spectrum that include a plurality of bands including at least the C-band and one or more additional bands, segmenting the plurality of bands by distance based on different transmission specifications for the plurality of bands based on fiber types and amplifiers used for corresponding bands; and placing one or more channels on the optical fiber in a corresponding band of the plurality of bands based on a distance between nodes associated with each of the one or more channels. The segmenting is based on a metric that is a function of fiber type of the optical fiber and amplifier performance for amplifiers used in the plurality of bands.

CROSS-REFERENCE

The present disclosure is a continuation-in-part of U.S. patentapplication Ser. No. 17/082,218, filed Oct. 28, 2020, which is now U.S.Pat. No. 11,196,504, with an issue date of Dec. 7, 2021, the contents ofwhich are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to optical networking systemsand methods. More particularly, the present disclosure relates tosystems and methods that allow network nodes of an optical network tooperate within an extended spectral band of optical signals.

BACKGROUND

Generally, the fiber-optic communication industry is facing a capacitycrunch, driven by relentless bandwidth growth. Recent reports indicatethat growth rates ranging from about 26% to about 37% are expected. Muchof this traffic growth is expected between users and data centers andbetween one data center and another.

Given these network bandwidth growth trends, the fiber-opticcommunication industry is focused on coming up with Capital Expenditures(CapEx) and Operating Expenditure (OpEx) efficient solutions. Forexample, there seems to be at least five hardware-centric options, eachwith their own associated tradeoffs, being pursued by the industry.

A first option for handling the increased growth in optical networksincludes converting fixed-grid optical line systems to flexible gridsystems, which has been a fast and simple way to obtain a short-termboost (e.g., about 20%) in capacity via improved spectral utilization.However, this expansion option has essentially been exhausted incommercial equipment, and network deployments of this equipment areproceeding apace.

A second option includes employing parallel optical line systems viaeither separate fiber strands or multi-core fiber Spatial DivisionMultiplexing (SDM). This option provides additional resilience againstfiber or line system component failures.

A third option includes increasing the channel spectral efficiency usinghigher order modulation constellations. However, this option hasdiminishing returns since the addition of each two extra bits (i.e., alinear increase) results in about 3.5 dB decrease in reach performance(i.e., an exponential decrease).

A fourth option includes considering network infrastructures that mightincrease the Signal-to-Noise Ratio (SNR) or Optical SNR (OSNR). Forexample, some research is directed to the use of Ultra-Low-Loss (ULL)fibers. Given a fixed amplifier spacing and complete fiber replacement,a difference between conventional Single-Mode optical Fiber (SMF) (i.e.,about 0.2 dB/km) and a ULL fiber (i.e., about 0.1424 dB/km) is about 4.6dB, which produces about a 3 dB gain in SNR. Unfortunately, though,expected capacity gain (e.g., about 20%) is a one-time benefit,sufficient for about six months' worth of traffic growth.

A fifth option includes accessing an expanded fiber spectrum from C-band(i.e., 1530 nm to 1565 nm) to an extended C-band to include L-band(i.e., 1565 nm to 1625 nm). This option affords a more significantcapacity increase of over 100% with a modest increase in line systemcost and propagation penalty. Since this option appears to providebetter results, the industry has moved toward solutions that operatewithin an extended band, particularly the amplification of opticalsignals within this extended band that are transported throughout anoptical network.

However, the current state of extended band amplification systems (e.g.,utilizing extended C-band and/or extended L-band) suffers from a lack ofinfrastructure in the field. Thus, to implement these extended bandsolutions, potentially expensive developments would be needed. Also,other issues have arisen with respect to the incorporation of thistechnology in optical networks.

Presently, companies providing optical services have indicated that theyare reluctant to invest in the development of certain modules (e.g.,Wavelength Selective Switching (WSS) components, Optical ChannelMonitoring (OCM) components, contentionless WSS (CWSS) components,tunable filters, etc.) that could cover the extended spectral range.Although amplifiers may be relatively easy to design and build, therewould normally be a delay in the availability of other modules (e.g.,WSS components, etc.). It appears that there are currently no programsthat have kicked off in this regard to incorporate this neededinfrastructure to operate within the extended band.

Therefore, cost is usually restrictive in the development of extendedband systems. Lower volumes (at least initially) will result in premiumcosts up front. Amplifier costs would increase due to extra powerrequired to support the additional spectrum and to overcome the GainFlattening Filter (GFF) losses. Also, Raman amplification would requirean extra pump to avoid compromising gain and ripple. Therefore, there isa need in the field of optical communication networks to provide systemsfor handling the ever-increasing demand and to provide systems that canbe implemented in a cost-effective way.

BRIEF SUMMARY

The present disclosure pertains to various systems and methods forextending the spectrum of optical channels. The C-band spectrum includesa band of wavelengths ranging from about 1530 nm to about 1565 nm and iscommonly used for the transmission of optical signals. Some systems arebeing developed that not only operate in the C-band but are alsoconfigured for operating in the L-band, which includes an additionalband of wavelengths ranging from about 1565 nm to about 1625 nm.However, the C+L band systems typically require separate transmissionequipment for each of the separate bands. Therefore, the presentdisclosure provides systems in which the same equipment can be used foran “extended” band, whereby the extended band includes the C-bandwavelength channels plus additional channels less than the entireL-band, as well as to shorter wavelengths in the S-band but notincluding the entire S-band. In this respect, the new spectrum describedherein may be referred to as an “extended C-band.” The extended C-bandmay push the bandwidths beyond just the C-band wavelengths to includewavelengths higher than the C-band (within part of the L-band) andwavelengths lower than the C-band (within part of the S-band). In someimplementations, the spectrum may be expanded to includes wavelengthsfrom about 1524 nm to about 1577 nm.

According to one implementation of the present disclosure, a methodincludes the step of establishing an extended optical spectrum having aplurality of optical channels for transmission of optical signals withinan optical network. The extended optical spectrum may include at leastthe C-band plus one or more sub-bands, the C-band having a range ofwavelengths from about 1530 nm to about 1565 nm. Each of the one or moresub-bands may have a range of wavelengths including at least one opticalchannel outside the range of the C-band. The method further includes thestep of segmenting the extended optical spectrum into a local band andan express band having different transmission specifications. The localband may be configured for transmission of optical signals between nodeshaving a relatively shorter distance therebetween. The express band maybe configured for transmission of optical signals between nodes having arelatively longer distance therebetween. The combination of the one ormore sub-bands covers less than the L-band having a range of wavelengthsfrom about 1565 nm to about 1625 nm and/or less than the S-band having arange of wavelengths from about 1460 nm to about 1530 nm.

According to another implementation of the present disclosure, a tunableedge filter may be configured to establish an extended optical spectrumhaving a plurality of optical channels for transmission of opticalsignals within an optical network. The extended optical spectrum mayinclude at least the C-band plus one or more sub-bands, where the C-bandhas a range of wavelengths from about 1530 nm to about 1565 nm. Each ofthe one or more sub-bands may have a range of wavelengths including atleast one optical channel outside the range of the C-band. The tunableedge filter may be further configured to segment the extended opticalspectrum into a local band and an express band having differenttransmission specifications. The local band may be configured fortransmission of optical signals between nodes having a relativelyshorter distance therebetween, and the express band may be configuredfor transmission of optical signals between nodes having a relativelylonger distance therebetween. The combination of the one or moresub-bands may cover less than the L-band having a range of wavelengthsfrom about 1565 nm to about 1625 nm and/or less than the S-band having arange of wavelengths from about 1460 nm to about 1530 nm.

According to yet another implementation of the present disclosure, anode operating in an optical network in provided. The node may includean add/drop device configured to add and drop optical channels within anextended optical spectrum having a plurality of optical channels fortransmission of optical signals within the optical network. The extendedoptical spectrum may include at least the C-band plus one or moresub-bands, wherein the C-band has a range of wavelengths from about 1530nm to about 1565 nm. Each of the one or more sub-bands may have a rangeof wavelengths including at least one optical channel outside the rangeof the C-band. The node further includes a filter for segmenting theextended optical spectrum into a local band and an express band havingdifferent transmission specifications, wherein the local band may beconfigured for transmission of optical signals between nodes having arelatively shorter distance therebetween, and the express band may beconfigured for transmission of optical signals between nodes having arelatively longer distance therebetween. The combination of the one ormore sub-bands may be configured to cover less than the L-band having arange of wavelengths from about 1565 nm to about 1625 nm and/or lessthan the S-band having a range of wavelengths from about 1460 nm toabout 1530 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings. Like reference numbers are used todenote like components/steps, as appropriate. Unless otherwise noted,components depicted in the drawings are not necessarily drawn to scale.

FIG. 1A is a diagram illustrating a first extended optical spectrumhaving multiple segments of optical sub-bands, according to variousembodiments of the present disclosure.

FIG. 1B is a diagram illustrating a second extended optical spectrumhaving multiple segments of optical sub-bands, according to variousembodiments of the present disclosure.

FIG. 2 is a diagram illustrating a portion of an optical network where afirst network node transports optical signals consuming channels in botha local band and an express band of an extended optical spectrum to asecond network node, according to various embodiments of the presentdisclosure.

FIG. 3 is a diagram illustrating the portion of the optical network ofFIG. 2 from a perspective of the entire extended optical spectrum,according to various embodiments of the present disclosure.

FIG. 4 is a diagram illustrating a segmented band transmission system,according to various embodiments.

FIG. 5 is a flow diagram illustrating a process for creating an extendedoptical spectrum, according to various embodiments.

FIG. 6 is a diagram illustrating a third extended optical spectrumhaving multiple optical sub-bands, according to various embodiments ofthe present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to systems and methods for extending orexpanding the spectral band for transporting optical signals within anoptical communication system. There has been a push in the opticalnetworking industry towards creating an extended band to increase thenumber of optical channels. Also, one focus of the present disclosure isto extend the optical spectrum for amplified transport systems.

Research in the field of extended band amplification has led to varioussystems using similar extended band concepts. Some solutions haveincluded Raman-based extended bandwidth amplification line systems.Current Reconfigurable Optical Add/Drop Multiplexing (ROADM) componentsand Wavelength Selective Switching (WSS) components are traditionallydesigned to only operate inside the conventional C-band (i.e., awavelength range from about 1530 nm to about 1565 nm). Since thesecomponents are generally designed only for this range, extension of theoperational band would be expensive and may still take years toimplement. Also, rare earth doped fiber amplifiers (e.g., Erbium-DopedFiber Amplifiers (EDFAs)) normally have Gain Flattening Filters (GFFs)which are much more difficult to produce if the bandwidth coverage isextended. The extended band also negatively impacts the amplifier NoiseFigure (NF) and gain ripple performance, and drives up the pump powerrequirements, thus making the EDFA less efficient.

In addition, extended band WSS components are possible to manufacture,but there is a balance between the number of pixels in the switchingelements, the band of operation, and the effective filtering resolutionwhich drives up WSS cost as the bandwidth increases. Also, as a result,the performance of the device may typically decrease. Modemmicro-amplifiers may have different NFs across extended bandwidth.Micro-amplifiers may be single channel amplifiers and may be configuredto cover only a portion of the system spectrum occupied by the modem. Insome implementations, the micro-amplifiers do not need spectralflattening. Raman amplification may require extra pumps and may starthaving issues with overlap of Raman pump and data signal wavelengths.

Regarding performance and capacity, most system vendors today haveimplemented modems that operate across about 4.8 THz of the C-bandspectrum (e.g., about 191.2 THz to about 196.0 THz). Going from about4.8 THz to about 6.0 THz would be a 25% increase in available spectrum.Amplifier Noise Figures (NFs) and gain ripple would increase appreciablydue to the number and depth of the GFFs. Modem micro-amps would alsosuffer from some amount of NF penalty. Even with additional GFFs, theripple would be larger than existing amplifiers, which results in anOptical Signal-to-Noise Ratio (OSNR) penalty. Also, WSS bandwidth woulddegrade proportionally with the spectral range increase due to LiquidCrystal on Silicon (LCoS) resolution, although this issue could beaddressed with next generation LCoS technology, which may still be yearsaway.

One solution for extending the optical band can be found in a relatedpatent (U.S. Pat. No. 8,280,258) having at least one common inventor,the disclosure of which is incorporated by reference herein. This issuedpatent anticipated the use of an extended band, where the opticalspectrum can by partitioned into “express” and “local” components, wherelocal transmission includes sending optical signals to an adjacent nodelocated a relatively shorter distance away, while express transmissionincludes sending optical signals to an adjacent node located arelatively longer distance away. Some embodiments may be configured toplace Optical Phase Conjugation into the “express” path to managelong-reach nonlinear effects. The present disclosure continues theseconcepts and includes further developments in this field, such as, forexample, a one-band system and an overlapping sub-band system, asdescribed below.

By providing an extended spectrum and splitting the spectrum into“express” and “local” band, the express paths can be used herein toavoid the limitations outlined above with respect to conventionalsystems. In the present disclosure, ROADMs and associated components canbe used only in the local path and over the currently defined C-bandspectrum. Optimal optical power density is somewhat independent of reach(i.e., about the same in both paths). Optimal optical power density isalso somewhat independent of the modulation format, although achievablereach may be sensitive to constellation cardinality.

In an example, an optical network is an optical communication systemserving various locations across a geography, e.g., North America. Itmay be noted that smaller networks (e.g., European optical networks) mayprovide more opportunities for implementing the extended band systemsand methods described in the present disclosure, particularly forseparating express and local channels. However, even continental-sizedNorth American networks may provide sufficient opportunity forimplementing a reasonable separation between express and localconnections. Additionally, such network configuration could be a goodfit for global cloud networks, which may need high-capacity “express”connections between centralized data center locations.

The optical network includes a plurality of nodes and in a nationwidenetwork (U.S.), the major inter-node distances may be about 500 to 1000km. The distance across North America is about 4000 km. The opticalnetwork would intuitively benefit from long optical reach andtransparency.

The major driver for extended band operation is the efficient use of thetransmission fiber asset. Since spectral efficiency gains are slowing asthe transponder encoding and decoding technologies approach the ShannonLimit, the capacity per fiber is not expected to increase significantlywithout an increase in the useable transmission bandwidth. One optionfor extended band in the transmission fiber is the use of all-Ramanamplification. A limitation of an all-Raman extended band system,however, is the ability to provide bulk gain elements for ROADMcomponents, add/drop components, and transponders/modems/transceivers.As noted above, designing EDFAs with the same bandwidth as an all-Ramantransmission portion would be expensive and complex and may result ininferior noise performance.

Nevertheless, the present disclosure is directed to advancing theextended band concept by introducing various novel features. The systemsand methods described in the present disclosure may include embodimentsthat can be grouped into two categories based on the approach taken tosegregate the band. A first category may be referred to as a “one-bandsystem” and the second category may be referred to as an “overlappingsub-band system.”

One-Band System

The “one-band system” may include a setup where EDFAs and/or Ramanamplifiers cover a continuous spectrum. The EDFAs and Raman amplifiersdo not need to cover the same spectrum, as indicated below regarding anexpress gain ripple being outside of a ROADM window that can beequalized by a separate Dynamic Gain Equalization (DGE) module.

In the one-band system, a tunable filter (e.g., an edge filter or fixedfilter) can be used to split the overall spectrum into express and localbands. The local band may serve shorter connections with fewer spans andmay include less expensive (lower performing) amplifiers, such asSemiconductor Optical Amplifiers (SOAs).

Also, the express band, in some embodiments, may be further split into“normal-express” and “ultra-express” sub-bands. A Gain Flattening Filter(GFF) may be used to provide tighter flatness specifications in theexpress band. The flatness characteristics may have looserspecifications in the local bands. This may result in a simplified GFFdesign, reduced costs, and reduced insertion loss, thereby improvingNoise Figure (NF) especially in the express portion of the band.

In some preferred embodiments, the express channels may be placed inlonger wavelengths if the stimulated Raman pumping is beneficial, asinduced by co-propagating “local” channels. When external Raman pumpsare used, the pump wavelengths may be arranged to provide gain toexpress channels, thereby minimizing overall system cost and power.Although gain tilt in the transition regions may be a problem, this maybe mitigated by ROADM channel power control. Also, express gain ripplemay be outside of a ROADM window, equalized by a separate DGE module.

Thus, the one-band system can include different components acrossdifferent portions of the one band. Also, local and express (as well asnormal-express and ultra-express) traffic can be segmented in differentportions on the one band, as described herein.

Overlapping Sub-Band System

The overlapping sub-band system may be split into two functionalsegments: a) extended-band transmission and b) photonic functions (e.g.,ROADM, add/drop, and transponder functions), where the photonicfunctions require bulk amplification. The photonic functions may beseparated into sub-bands where each sub-band is a portion of the fullband. In some cases, each sub-band may overlap in frequency (wavelength)with at least one other sub-band. The purpose for this overlap may be toallow for the design of bulk amplifiers (e.g., EDFAs), which providehigh performance and high efficiency in each sub-band of interest. Itmay be difficult to create an EDFA with a gain region which dropssharply at the edges of the band. By allowing the sub-bands to overlap,this restriction is essentially eliminated. When channels from differentspectral sub-bands are split and then recombined, the spectrum can befiltered to prevent Multi-Path Interference (MPI) or cross-talk fromother sub-bands. While the sub-bands are spatially separated intoparallel sub-band paths inside “photonic functions,” the spectrum, insome cases, may not need to be sharply truncated. However, suchtruncation can be performed when the spatial paths are recombined, i.e.,via tunable filters, as described below.

In the overlapping sub-band system, the WSS technology may follow thesame or similar design paradigm. The cost tradeoff of multiple WSSmodules vs. a single wideband module is not as strong as the EDFAmodules, but this is expected to be offset at the system level byallowing the system to selectively deploy only the WSS modules neededfor the processed sub-bands at a given site.

The transponders/modems/transceivers in the overlapping sub-band systemcan also be designed in sub-bands thereby simplifying the micro-EDFAdesign and retaining the noise performance within those bands.

The overlap in the gain ranges of the sub-bands does require filteringat the system boundary between sub-band photonics and the extended bandtransmission to prevent crosstalk and multipath interference. This isachieved through a combination of the WSS modules in combination withtwo or three port optical filters.

Operating Principles

FIG. 1A shows a representation of a first extended optical spectrum 20Afor the transmission of optical signals. The optical spectrum 20A may beviewed as being “extended” in the sense that it extends beyond thenormal C-band (e.g., about 1530 nm to about 1565 nm) range. According tovarious embodiments of the present disclosure, the extended opticalspectrum 20A may then be partitioned into certain sub-bands. Forexample, the extended optical spectrum 20A may include a “local”sub-band 22 and an “express” sub-band 24. The local sub-band 22 mayinclude a conventional ROADM passband, which may include up to 88optical channels divided into 50 GHz bands and may be similar to or thesame as the frequency range of the C-band (e.g., about 191.2 THz toabout 196.0 THz). Also, the local sub-band 22 may include ROADM-basedcollector and grooming. In some embodiments, the express sub-band 24 mayinclude up to about 40 channels divided into 50 GHz bands. The expresssub-band 24 may be band-based and may be ungroomed.

The express sub-band 24 may be separated from the local sub-band 22 byusing a tunable passband filter. In some embodiments, the tunablepassband filter may be configured to further divide the express sub-band24 into multiple additional sub-bands, as depicted in FIG. 1B. Forexample, from the channels of the express sub-band 24, the tunablepassband filter may divide the express sub-band 24 at least into a“normal-express” sub-band 24A and an “ultra-express” sub-band 24B.According to some embodiments, the ultra-express sub-band 24B mayinclude wavelengths that are separated from the local sub-band 22 by thenormal-express wavelengths.

Thus, the embodiments of the present disclosure may use a tunable filter(e.g., an edge filter) to separate the local sub-band 22 from theexpress sub-band 24 (or express sub-bands 24A, 24B). The filtering mayoccur at express nodes in the network, which may include those nodesthat are more greatly separated from other nodes in the network. Also,express channels can be bypassed in local nodes. The tunable edge may bealigned at the edge of conventional C-band (e.g., at about 1565 nm). Theedge may be defined by the ROADM boundary, but may also overlap with theconventional ROADM passband. In some embodiments, the edge may also beseparated by a dead zone gap, although this may be considered in somecases to be a waste of spectrum.

According to another embodiment, the second extended optical spectrum20B of FIG. 1B shows the local sub-band 22 and the express sub-bands24A, 24B. Also, the extended optical spectrum 20B may include a lowersub-band 26 having wavelengths lower than the local sub-band 22including channels of the C-band. In this respect, the wavelengths ofthe extended optical spectrum 20B may extend from both ends of theC-band, where the lower sub-band 26 includes shorter wavelengths (andhigher frequencies) than the C-band and the express sub-bands 24A, 24Binclude longer wavelengths (and lower frequencies) than the C-band.

According to the various embodiments of the present disclosure, aconventional C-band (i.e., about 1530 nm to 1565 nm) could be extendedto an extended band (or super C-band). For example, the extended bandmay range from about 1524 nm to about 1577 nm. In this case, the lowersub-band 26 may include wavelengths ranging from about 1524 nm to 1530nm. The local sub-band 22 may include wavelengths ranging from about1530 nm to about 1565 nm. Also, the express sub-bands may includewavelengths ranging from about 1565 nm to about 1577 nm.

The extreme regions of this extended optical spectrum 20A, 20B, whichmay include one or more of sub-bands 22, 24, 24A, 24B, 26, may includeoperating specifications that may be higher than the specifications forthe C-band range (e.g., the local sub-band 22). With higherspecifications, these sub-bands may be used for allowing express trafficto flow under the higher specifications. For example, the amplificationin sub-bands 24, 24A, 24B, 26 may have greater performance thanamplification in the local sub-band 22.

The magnitude to which the extended band may be extended may be factorof the size of the network and how far apart the various nodes arepositioned from each other. For example, if a large percentage of thenetwork nodes are located far apart, thereby benefiting fromcommunication along the express sub-bands 24A, 24B, then the extendedband may be extended by a larger amount. However, if a low percentage ofthe network nodes are located far apart (e.g., such as in some Europeannetworks), then the extended band may be extended to a lesser amountsince most traffic may be considered to be local traffic. Thus, therange of the entire extended spectrum may be modified as neededaccording to how many channels may be needed for express traffic (andhow many channels may sufficiently be used for local traffic).

The better transmission specification may be given to the extremes ofthe extended optical spectrums 20A, 20B, which may include, for example,the express sub-bands 24, 24A, 24B and, in some embodiments, may furtherinclude the lower sub-band 26. For instance, the better transmissionspecifications may include lower loss in the fibers, better (lower)Noise Figures (NFs), etc. Also, Raman amplifiers may be configured tooperate better in the extremes of the extended optical spectrums 20A,20B. Also, the Stimulated Raman Scattering (SRS) losses may be based ona narrower spectrum and may be less in the extremes.

The local sub-band 22 may correspond to part or all of the C-band, whichincludes frequencies ranging from about 195.90 THz to about 191.55 THz,which may include 88 channels each spaced by 50 GHz. These frequenciescorresponding to wavelengths ranging from about 1530 nm to about 1565nm. The express sub-band 24 and/or express sub-bands 24A, 24B mayinclude wavelengths ranging from about 1565 nm to about 1577 nm.

FIG. 2 is a diagram illustrating an embodiment of a portion 30 of anoptical network where a first node 32 transports optical signalsconsuming channels over the entire extended spectrum (e.g., the firstextended optical spectrum 20A, the second extended optical spectrum 20B,or other suitable extended range). Thus, transmission is made in boththe local sub-band 22 (e.g., C-band) and any additional sub-bands (e.g.,express sub-bands 24, 24A, 24B, lower sub-band 26, etc.) to a secondnode 34.

Optical signals are transported over a transmission fiber 36 havingmultiple spans, including the local sub-band 22 and express sub-band 24.The first node 32 includes a ROADM 38 that operates in a conventionalmanner for transmitting and receiving C-band spectrum signals with“local” nodes. For transporting optical signals over the transmissionfiber 36, the first node 32 includes a tunable edge add component 40, anexpress channel multiplexer 42, and a post-amplifier 44. The signals aretransmitted over the transmission fiber 36 and received by the secondnode 34. The second node 34 includes a pre-amplifier 46, a tunable edgedrop component 48, an express channel demultiplexer 50, and a ROADM 52.

The tunable edge add component 40 and the tunable edge drop component 48may be referred to as “tunable edge filters” and may be configured totune the respective node for operation in one or more of the sub-bandsdescribed with respect to FIGS. 1A and 1B. Also, the tunable edge addcomponent 40 and the tunable edge drop component 48 may include anadd/drop device for adding and/or dropping channels based on thesub-bands to which the tunable edge filter is tuned when located at anexpress node. According to some embodiments, a network node may includeboth a filter (e.g., tunable edge filter) and an add/drop device foradjusting to the particular extended band in which the node isconfigured to operate. The tunable edge add component 40 and the tunableedge drop component 48 may include a bypass function such that expresschannels bypass ROADM components 38 and 52 when located at a local node.

It should be noted that FIG. 2 shows the transmission of signals in asingle direction (i.e., from the first node 32 to the second node 34).However, it should be understood that communication may bebi-directional, where the second node 34 may transmit signals in theopposite direction over the transmission fiber 36 to the first node 32.In this respect, the first and second nodes 32, 34 may each include thecomponents for receiving or transmitting, respectively, described withrespect to the other node.

The ROADM 38 of the first node 32 provides add/drop functionality for“local” channel spectrum coverage. The tunable edge add component 40 ofthe first node 32 is configured to define the separation of the opticalspectrum 20 into the two or more sub-bands (e.g., local sub-band 22 andexpress sub-band 24). The express channel multiplexer 42 may be alow-cost, static component implemented using Arrayed-Waveguide Grating(AWG) filters. Alternatively, the express channel multiplexer 42 can bea more complex WSS-based structure, but with WSS components required tocover only a limited spectrum range.

The second node 34 includes the tunable edge drop component 48 forremoving the express channels and sending these express channel signalsto the express channel demultiplexer 50 for processing. The localchannels separated by the tunable edge drop component 48 are provided tothe ROADM 52 for normal processing of the local channels.

In this embodiment, the first node 32 may use the same components acrossthe entire extended spectrum 20A, 20B. However, according to theimplementations described in the present disclosure, these componentsmay be utilized in a way where the filtering procedure includessegmenting the spectrum into two or more sections having differentspecifications (e.g., Noise Factor (NF), gain ripple, etc.). Therefore,instead of attempting to maintain the same specifications for eachpartial spectrum, the components may be modified from conventionalcomponents to allow them to either operate over the entire extended bandor to split them up to operate over one (or more) of the partialspectrums.

According to some embodiments, the channels (e.g., channels of the localsub-band 22) having higher specifications (e.g., less noise and gainripple) may be allocated for regions of the network having a longerreach, which may include the additional channels (e.g., channels insub-bands 24, 24A, 24B, 26) at the extremes of the extended band. Also,the local sub-band 22 may include channels that are allocated forshorter reach applications. For example, a longer reach application(e.g., Boston to Chicago) for connection between nodes that are locatedrelatively farther apart may be configured to operate with the expresssub-band 24, while a shorter reach application (e.g., Philadelphia toNew York) for connection between nodes that are located relativelycloser together may be configured to operate with the local sub-band 22.The lower sub-band 26 may be grouped with express sub-bands or the localsub-band 22 and thereby may be allocated as either express band or alocal band.

The tunable edge add component 40 and tunable edge drop component 48 maybe configured as WSS components for add/drop functions with the addedfunctional characteristic of enabling a tunable filtering process tosplit the continuous extended band into sub-bands for operation withinone or more of the sub-bands. The express channels (e.g., sub-bands 24,24A, 24B, 26) can be added by the express channel multiplexer 42 anddropped by the express channel demultiplexer 50. The filters of thetunable edge add component 40 and tunable edge drop component 48 may beconfigured to split the continuous spectrum or split one of thesub-bands (e.g., express sub-band 24).

FIG. 3 is a diagram showing the portion 30 of the optical network shownin FIG. 2 from a perspective of the entire optical spectrum as extendedwith respect to the various embodiments of the present disclosure. Asshown in FIG. 3, the portion 30 may include bi-directional communicationbetween a first express node 62 and a second express node 64.Communication between adjacent pairs of nodes 62A, 62B, 62C, 62D mayinclude an extended spectrum 66, which includes a local band 68 and anexpress band 70. Handling of local channels in the local band 68 can beperformed separately from the handling of express channels in theexpress band 70.

Each node 62A, 62B, 62C, 62D is capable of processing both localchannels and express channels. In this example, the first (express) node62A includes an add/drop component 72 for multiplexing anddemultiplexing channels in both the local band 68 and the express band70. A local add/drop component 74 of the second (local) node 62B isconfigured for multiplexing and demultiplexing channels in just thelocal band 68. Similarly, the third (local)node 62C includes a localadd/drop component 76 for multiplexing and demultiplexing channels injust the local band 68. The fourth (express) node 62D includes anadd/drop component 78 for multiplexing and demultiplexing channels inboth the local band 68 and the express band 70. The add/drop components72, 74, 76, 78 connect the corresponding ROADM components 80A, 80B, 80C,80D in the local band 68 and the Thin Optical Add/Drop Multiplexing(TOADM) components 92A, 92D in the express band 70 and also connect tocorresponding transceivers 82, 84, 86, 88, respectively.

In an example where nodes 62A and 62D are considered to be “express”nodes and nodes 62B and 62C are considered to be “local” nodes, theexpress nodes 62A, 62D use the TOADM components 92A, 92D for add/dropwhile the local nodes 62B, 62C use the TOADM components 92B, 92C forbypass of the express channels. The express channels will bypass theROADM components 80B, 80C at the local nodes 62B, 62C, but will beadded/dropped by the ROADM components 80A, 80D at the express nodes 62A,62D.

The overall system of the portion 30 of the optical network includes aDynamic Gain Equalizer (DGE) element 100, which covers exclusively theexpress band 70, as shown in FIG. 3. Spectrum equalization on the localband 68 may be accomplished conventionally through the ROADM components80.

In some embodiments, the express add/drop components 72, 78 may beconfigured as WSS components for operations with the ROADM components 80and/or TOADMs 92. The express add/drop components 72, 78, according tovarious embodiments, may include reflective ports that are notcontrolled. The reflective ports may have flat reflective surfaces thatare configured to reflect to a single port. Thus, the channels outsideof the normal control pixels for the components 72, 78 may fully reflectoff the reflective surfaces to the single port. This reflectivecharacteristic may be applied to other bands or sub-band regions bycausing outside channels to reflect to one port. For example, the unusedchannels may be reflected to the express band. The rest of the channels(e.g., in-band channels) may be pixelized by the corresponding ROADMcomponent 80.

FIG. 4 is a diagram illustrating an embodiment of a segmented bandtransmission system 110 for transmission of extended band opticalsignals between a first express node 112 and a second express node 114.The first express node 112 includes a full-band amplifier device 116configured for amplifying the entire extended band (e.g., opticalspectrum 20A, 20B) from output ports of the first express node 112. Theoptical signals amplified by the full-band amplifier device 116,associated with the first express node 112, are transmitted to afull-band amplifier device 118 associated with the second express node114. In the opposite direction, optical signals from the second expressnode 114 are amplified by post-amplifier elements of the full-bandamplifier device 118 and transmitted to the first express node 112having pre-amplifier elements of the full-band amplifier device 116.Also, intermediate nodes or line amplifiers are positioned between thenodes 112, 114 and may include one or more full-band amplifiers. In FIG.4, two intermediate full-band amplifier devices 120, 122 are shown.

The full-band amplifier devices 116, 118, 120, 122 are configured asbi-directional devices and are configured to amplify the optical signalscovering the entire extended spectrum (e.g., 20A, 20B), which mayinclude the C-band plus additional wavelengths. The express nodes (e.g.,second express node 114) may further include a sub-band amplifier 124having filtering for processing of local and/or express signals. Thefilters of the sub-band amplifier 124 may be connected to sub-bandcomponents 126 (e.g., amplifiers, WSS components, etc.) for handlinglocal channels of the optical spectrum.

The sub-band components 126 (e.g., amplifiers, WSSs, etc.) may beimplemented with Rare-Earth Doped Fiber Amplifiers (REDFAs), SOAs,and/or Raman amplifiers. For sub-band applications, the REDFAs may beconfigured as micro-REDFAs that maintain noise performance with therespective sub-band. However, in the “one-band” application, thecomponents may be configured to extend across the whole band, where theperformance of the band is segregated with different specifications.Some components may be configured for full-band transmissions, whileothers may be configured to transmit over only a portion (e.g., one ormore the sub-bands 22, 24, 24A, 24B, 26) of the entire spectrum. Itshould also be recognized that the components may be configured tooperate in sub-bands that overlap with other sub-bands and/or mayoperate such that the components themselves have overlapping ranges thatoverlap at any points along the entire spectrum.

The embodiments of the present disclosure may include certain advantagesover conventional system. For example, it may be noted that the presentdisclosure provides an option for Service Providers (SPs). For a smallnetwork (e.g., a European network), the present disclosure offers anoption to separate express and local channels from each other forprocessing in two different ways. However, even continental-sizednetworks (e.g., a North American network) may provide sufficientopportunity for implementing a reasonable separation between local andexpress connections.

Also, the embodiments of the present disclosure may also be utilized byGlobal Cloud Providers. As such, the disclosed network configuration maybe a good fit for Global Cloud Network companies, which may needhigh-capacity express connections between centralized data centerlocations.

When extending these optical wavelength bands, there may inherently be arange of performance across the spectrum that necessitates a need todifferentiate traffic to particular bands based on performance. Thepresent disclosure targets practical system-level design considerations(not lab-type concepts) with cost and complexity being some of theimportant parameters to consider in the creation of the extendedspectrum.

FIG. 5 is a flow diagram illustrating an embodiment of a process 130 forcreating an extended optical spectrum for use in an optical network. Inthis embodiment, the process 130 may include the step of establishing anextended optical spectrum having a plurality of optical channels fortransmission of optical signals within an optical network, as indicatedin block 132. The extended optical spectrum may include at least theC-band plus one or more sub-bands, where the C-band has a range ofwavelengths from about 1530 nm to about 1565 nm. Each of the one or moresub-bands may have a range of wavelengths including at least one opticalchannel outside the range of the C-band. The process 130 may furtherinclude the step of segmenting the extended optical spectrum into alocal band and an express band having different transmissionspecifications. The local band may be configured for transmission ofoptical signals between nodes having a relatively shorter distancetherebetween, and the express band may be configured for transmission ofoptical signals between nodes having a relatively longer distancetherebetween. In some embodiments, a combination of the one or moresub-bands may cover less than the L-band, which has a range ofwavelengths from about 1565 nm to about 1625 nm.

According to additional embodiments, the process 130 may be furtherdefined, whereby the combination of the one or more sub-bands may coverless than half of the L-band. The one or more sub-bands may include alower sub-band having a wavelength range with wavelengths less than theC-band, whereby the wavelength range of the lower sub-band may be lessthan half the range of wavelengths of the C-band. The step ofestablishing the extended optical spectrum may include establishing arange of wavelengths from about 1524 nm to about 1577 nm.

The process 130 may also be defined such that the specifications includeone or more of Noise Factor (NF) and gain ripple. The transmissionspecifications of the express band may enable the optical signalstransmitted by way of the express band to have a longer reach than thelocal band. The step of segmenting the extended optical spectrum mayinclude segmenting bands that overlap.

The process 130 may further comprise the step of segmenting the expressband into a normal express band and an ultra-express band, wherein theultra-express band enables a longer reach than the normal express band.Also, the process 130 may further include the step of modifying theoperating parameters of a plurality of optical components of a networknode to enable the network node to operate over the extended opticalspectrum. The process 130 may also include the step of enabling one ormore of the optical components to operate over the entire extendedoptical spectrum and the step of enabling one or more others of theoptical components to operate over one of the express bands and thelocal band.

FIG. 6 is a diagram illustrating a third extended optical spectrumhaving multiple optical sub-bands, according to various embodiments ofthe present disclosure. In particular, compared to FIGS. 1A-1B, FIG. 6illustrates the complete optical fiber transparency window, along withcorresponding amplifier types for each sub-band. Of note, the variousapproaches for segmenting optical spectrum into local, express,ultra-express, etc. bands are contemplated with the extended opticalspectrum, i.e., the complete optical fiber transparency window.

The complete optical fiber transparency window is as follows (note, thewavelength values are approximate):

O-band 1260-1360 nm E-band 1360-1460 nm S-band 1460-1530 nm C-band1530-1565 nm L-band 1565-1625 nm U-band 1625-1675 nm

The E-band includes the so-called water peak with respect to opticalloss in the complete optical fiber transparency window. The C-bandincludes the lowest attenuation and is the original and mostly used bandin DWDM deployments. The L-band has the next lowest attenuation and isbeing used as an expanded DWDM band.

From an amplification perspective, there are various amplificationapproaches known in the art and they can be classified as rare earthdoped fiber, fiber Raman, and semiconductor. Types of rare earth dopedfiber amplifiers include silica-based EDFAs, fluoride-based EDFAs,tellurite-based EDFAs, fluoride-based thulium-doped fiber amplifiers(TDFAs), fluoride-based praseodymium-doped fiber amplifiers (PDFAs),P-doped silica bismuth-doped fiber amplifier (BDFA), low-Ge silica BDFA,high-Ge silica BDFA, etc. Types of fiber Raman amplifiers include silicaand tellurite-based amplifiers with different numbers of laser diodes(LD). Types of semiconductor amplifiers include linear opticalamplifiers (LOAs), quantum-well semiconductor optical amplifiers (SOAs),and quantum-dot SOAs. Of course, the present disclosure contemplatesemerging optical amplifier technologies. Also, of note, it is possibleto construct an amplified to cover the entire transmission region (e.g.,1270-1670 nm) using a combination of BDFAs and EDFAs; of course, anysubset is also contemplated.

The present disclosure contemplates using a plurality of the entirebands, O-band, E-band, S-band, C-band, L-band, and U-band, as well as asub-bands of the full bands or sub-bands across adjacent bands, in asegmented manner based on the reach of traffic, i.e., local, express,ultra-express, etc. The segmented manner is based in part on theperformance of the specific spectrum (e.g., from a loss perspective) andthe performance of the optical amplifiers in the specific spectrum. Forexample, if a band's amplifier has a naturally worse noise performance,or ripple performance, there is a worsening of the SpectralEfficiency*Reach product. This lends itself to treating each band orsub-band differently, reserving the longest reach for the best product.That is, the local, express, and ultra-express designations can be basedon the Spectral Efficiency*Reach product for each band or sub-band.

Of note, the Spectral Efficiency*Reach product can be a function of theoptical amplifier performance as well as the fiber performance, i.e.,different fiber types may have different performances in different bandsor sub-bands. For example, L-band may have better performance thanC-band for ultra-express in most fibers. Thus, L-band can be designatedfor ultra-express, C-band for express, and any of the remaining bandsfor local. Of course, sub-band combinations are also contemplated.

The Spectral Efficiency*Reach product is an example metric that can beused to base segmentation of the bands or sub-bands. Other metrics arealso contemplated such as Capacity*Distance (i.e., C*Z). Of note, thereis indeed strong historical precedent for this C*Z metric, and it isfrequently used in older papers which presented results far belowShannon limit and with fixed total spectral bandwidth (i.e., C-bandonly). Older usage (below Shannon limit, fixed spectral bandwidth) isquite useful, since results were primarily limited by trade-off betweenreceiver bandwidth versus noise accumulation, i.e., twiceCapacity˜2×noise*½ distance; C˜1/Z, where C stands for capacity and Zstands for distance. Hence C*Z could be assumed approximately constantunder a fixed system design, allowing for a convenient comparison ofsystem designs.

However, as optically amplified fiber-optic systems approach Shannonlimit, the relationship changes to Capacity˜log(Es/No) when Es/No>>1.With the same assumption of approximately linear noise accumulation overdistance, we get Capacity˜log(A/Z)=log(A)−log(Z), where A is constant.So, C+log(Z)˜constant. Thus, it takes very large decrease in channeldistance to make a small increase in capacity possible.

For the metric, an equivalent way of looking at it is that SpectralEfficiency (SE) is purely dictated by SNR as guided by ShannonSE=2*log₂(1+SNR) for a two orthogonal polarization waveguide. Distanceis being used, and has traditionally been used, as a proxy for noiseaccumulation (both linear and non-linear) which may not be strictly truein the case of systems with different fiber types and systems withdifferent span lengths but is a good estimate.

Optical fiber types are generally classified based on their dispersionoperation and referred to as non-dispersion shifted fiber (NDSF),dispersion shifted fiber (DSF), and non-zero dispersion shifted fiber(NZDSF). Of note, there are various types of NZDSF based on the zerodispersion wavelengths. An example of NDSF is SMF-28. Non-limitingexamples of NZDSF include Truewave and variants thereof, LEAF andvariants thereof, and the like. Again, the Spectral Efficiency*Reachproduct if a function of the fiber type and the amplifier performance.

As described herein, the terms bands and sub-bands can be usedinterchangeably to represent some portion of the optical spectrum. Thatis, a band does not necessarily mean the C-band, the L-band, etc., butcould be some arbitrary portion thereof as well as crossing over thesebands. The terms bands and sub-bands are just meant to denote someportion of the optical spectrum. Also, as described herein, segmentationcan be on a per band or sub-band basis but can also be within a band orsub-band, as well as extend across a band or sub-band. All suchembodiments are contemplated herewith.

Although the present disclosure has been illustrated and describedherein with reference to exemplary embodiments providing variousadvantages, it will be readily apparent to those of ordinary skill inthe art that other embodiments may perform similar functions, achievelike results, and/or provide other advantages. Modifications, additions,or omissions may be made to the systems, apparatuses, and methodsdescribed herein without departing from the spirit and scope of thepresent disclosure. All equivalent or alternative embodiments that fallwithin the spirit and scope of the present disclosure are contemplatedthereby and are intended to be covered by the following claims.

What is claimed is:
 1. A method comprising steps of: for operation on anoptical fiber in an optical network with the optical fiber havingextended optical spectrum that include a plurality of bands including atleast the C-band and one or more additional bands, segmenting theplurality of bands by distance based on different transmissionspecifications for the plurality of bands based on fiber types andamplifiers used for corresponding bands; and placing one or morechannels on the optical fiber in a corresponding band of the pluralityof bands based on a distance between nodes associated with each of theone or more channels.
 2. The method of claim 1, wherein the segmentingis based on a metric that is a function of fiber type of the opticalfiber and amplifier performance for amplifiers used in the plurality ofbands.
 3. The method of claim 1, wherein the plurality of bands includetwo bands and the segmenting includes a local band and an express band,the local band configured for transmission of optical signals betweennodes having a relatively shorter distance therebetween, the expressband configured for transmission of optical signals between nodes havinga relatively longer distance therebetween.
 4. The method of claim 1,wherein the plurality of bands include three bands and the segmentingincludes a local band, an express band, and an ultra-express band, thelocal band configured for transmission of optical signals between nodeshaving a relatively shorter distance therebetween, the express bandconfigured for transmission of optical signals between nodes having arelatively longer distance therebetween, and the ultra-express bandconfigured for transmission of optical signals between nodes having arelatively longer distance therebetween than the express band.
 5. Themethod of claim 1, wherein the one or more additional bands includes acombination of sub-bands covering less than the L-band having a range ofwavelengths from about 1565 nm to about 1625 nm and/or less than theS-band having a range of wavelengths from about 1460 nm to about 1530nm.
 6. The method of claim 1, wherein the segmenting is via a tunableedge filter.
 7. The method of claim 1, further comprising performinggain flattening filtering with tighter specifications in differentbands.
 8. The method of claim 7, wherein the C-band is used for a localband, and the one or more additional bands include an express band wherethe gain flattening filtering is performed with a dynamic gain equalizer(DGE) element.
 9. The method of claim 1, further comprising performingRaman amplifier in bands with longer distances based on the segmenting.10. The method of claim 1, further comprising utilizing a fixedmultiplexer and demultiplexer structure for an express band; andutilizing a wavelength selective switch for a local band.
 11. An opticalnode comprising: a tunable edge filter connected to an optical fiber inan optical network, wherein the tunable edge filter is configured tosegment an extended optical spectrum on the optical fiber into aplurality of bands including at least the C-band and one or moreadditional bands, wherein the plurality of bands are segmented bydistance based on different transmission specifications for theplurality of bands that are due to fiber types and amplifiers used forcorresponding bands, and wherein one or more channels are placed on theoptical fiber in a corresponding band of the plurality of bands based ona distance associated with each of the one or more channels.
 12. Theoptical node of claim 11, wherein the plurality of bands are segmentedbased on a metric that is a function of fiber type of the optical fiberand amplifier performance for amplifiers used in the plurality of bands.13. The optical node of claim 11, wherein the plurality of bands includetwo bands and the plurality of bands include a local band and an expressband, the local band configured for transmission of optical signalsbetween nodes having a relatively shorter distance therebetween, theexpress band configured for transmission of optical signals betweennodes having a relatively longer distance therebetween.
 14. The opticalnode of claim 11, wherein the plurality of bands include three bands andthe plurality of bands include a local band, an express band, and anultra-express band, the local band configured for transmission ofoptical signals between nodes having a relatively shorter distancetherebetween, the express band configured for transmission of opticalsignals between nodes having a relatively longer distance therebetween,and the ultra-express band configured for transmission of opticalsignals between nodes having a relatively longer distance therebetweenthan the express band.
 15. The optical node of claim 11, wherein the oneor more additional bands includes a combination of sub-bands coveringless than the L-band having a range of wavelengths from about 1565 nm toabout 1625 nm and/or less than the S-band having a range of wavelengthsfrom about 1460 nm to about 1530 nm.
 16. The optical node of claim 11,wherein gain flattening filtering with tighter specifications indifferent bands.
 17. The optical node of claim 16, wherein the C-band isused for a local band, and the one or more additional bands include anexpress band where the gain flattening filtering is performed with adynamic gain equalizer (DGE) element.
 18. The optical node of claim 11,further comprising a Raman amplifier in bands with longer distances thana local band.
 19. The optical node of claim 11, further comprising afixed multiplexer and demultiplexer structure for an express band; and awavelength selective switch for a local band.
 20. An optical networkcomprising: at least two nodes with optical fibers interconnecting anyof the at least two nodes; and one or more amplifier nodes between anyof the at least two nodes, each of the at least two nodes include atunable edge filter connected to an optical fiber in an optical network,wherein the tunable edge filter is configured to segment an extendedoptical spectrum on the optical fiber into a plurality of bandsincluding at least the C-band and one or more additional bands, whereinthe plurality of bands are segmented by distance based on differenttransmission specifications for the plurality of bands that are due tofiber types and amplifiers used for corresponding bands, and wherein oneor more channels are placed on the optical fiber in a corresponding bandof the plurality of bands based on a distance associated with each ofthe one or more channels.